Refuse incinerator plant design and method of operating such a plant

ABSTRACT

THERE IS DISCLOSED A MUNICIPAL INCINERATOR PLANT IN WHICH A HIGH PRESSURE STEAM BOILER IS SO ARRANGED THAT HOT COMBUSTION GASES FROM THE INCINERATOR ARE COOLED BY PASSAGE THERETHROUGH TO A TEMPERATURE COMPATIBLE WITH THE CONSTRUCTION MATERIALS OF DUST COLLECTING AND BLOWER EQUIPMENT THROUGH WHICH THE COMBUSTION GASES FLOW TO A STACK. SUCH GASES ARE THEREBY COOLED AND CLEANED WITHOUT WATER SPRAYS AND THE STEAM SO GENERATED IS IN PART CONVERTED INTO MECHANICAL ENERGY FOR OPERATION OF SOME COMPONENTS OF THE INCINERATOR SYSTEM. THE INCINERATOR STACK HAS CONCENTRIC INNER AND OUTER FLUES, AND THE HOT COMBUSTION GASES ARE DISCHARGED INTO THE INNER FLUE. A BLOWER, OPERATED BY THE HIGH PRESSURE STEAM, CIRCULATES AIR THROUGH A CONDENSER TO CONDENSE THE EXHAUST STEAM AND HEAT THE AIR. THE AIR SO HEATED IS DISCHARGED INTO THE OUTER CONCENTRIC FLUE SO THAT THE COMBUSTION GASES LEAVE THE STACK SURROUNDED BY AN ENVELOPE OF RISING CLEAN AIR, RESULTING IN THE PRODUCTS OF COMBUSTION BEING CARRIED HIGHER ABOVE THE STACK, ESPECIALLY IN PERIODS OF CALM AIR, BEFORE THEY DIFFUSE INTO THE ATMOSPHERE THAN WOULD OTHERWISE BE THE CASE. THE BLOWER ABOVE REFERRED TO IS DRIVEN BY A TURBINE WICH IS OPERATED AS A PRESSURE REGULATOR FOR THE HIGH PRESSURE STEAM GENERATED BY THE BOILER.

Sept. 21, 1971 B. B. REILLY REFUSE INCINERATOR PLANT DESIGN AND METHOD QF OPERATING SUCH A PLANT 2 Sheets-Sheet 1 Filed Sept. 8, 1969 PwN INVENTOR. BERT/7AM a. REILLY Attorneys P 21, 1971 B. B. REILLY 3,606,841

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BERTRAM 8. REILLY A f forneys United States Patent Int. Cl. F23g 5/00 US. Cl. 11010 8 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a municipal incinerator plant in which a high pressure steam boiler is so arranged that hot combustion gases from the incinerator are cooled by passage therethrough to a temperature compatible with the construction materials of dust collecting and blower equipment through which the combustion gases flow to a stack. Such gases are thereby cooled and cleaned without water sprays and the steam so generated is in part converted into mechanical energy for operation of some components of the incinerator system. The incinerator stack has concentric inner and outer fines, and the hot combustion gases are discharged into the inner flue. A blower, operated by the high pressure steam, circulates air through a condenser to condense the exhaust steam and heat the air. The air so heated is discharged into the outer concentric flue so that the combustion gases leave the stack surrounded by an envelope of rising clean air, resulting in the products of combustion being carried higher above the stack, espe cially in periods of calm air, before they diffuse into the atmosphere than would otherwise be the case. The blower above referred to is driven by a turbine which is operated as a pressure regulator for the high pressure steam generated by the boiler.

FIELD OF THE INVENTION This invention relates to municipal incinerators and is for an improved incinerator designed to avoid the use of large quantities of water commonly used in such incinerators, reduce present objection to such plants being located in populated areas, and more effectively dispose of the combustion gases and effect an economy in the operation through the use of waste heat, and also provide a novel method of disposing of combustion gases.

BACKGROUND OF THE INVENTION Municipal incinerator plants have heretofore been designed where the hot combustion gases from the incinerator are cleansed and cooled by passing them through water sprays, but this has certain objections, among which are the large water requirements due to evaporation and pollution of water so used, while the washed gases with their burden of evaporated water, upon leaving the stack, produce a dense visible plume of vapor that is assumed by the public to be much more objectionable than it is in fact. While the use of electrostatic gas cleaners has been proposed to clean the incinerator combustion products, the high temperature of these gases is destructive both to the precipitator and the succeeding gas withdrawal equipment. Also, it has heretofore been proposed to use waste heat boilers in connection with incinerator plants but without effective use of the steam in the operation of the incinerator. This is largely due to the non-uniform character of the combustible material comprising municipal waste and the variation in moisture content, resulting in a wide fluctuation in the rate of steam production.

SUMMARY OF THE INVENTION According to the present invention a high pressure steam boiler is located in the discharge outlet of the comace bustion chamber of an incinerator, as for example an incinerator of the type shown in my Pats. 2,983,234 and 3,199,474. By high pressure steam boiler, I contemplate pressures above 50 and preferably in excess of p.s.i. In passing through the boiler the gases yield much of their heat to generate high pressure steam, but they may nevertheless still be at a temperature too high for passage through the succeeding equipment, so that a blower is provided for introducing ambient air into the gases and dilute them to further reduce the temperature before they pass into an electrostatic dust cleaner. There is a suction fan at the discharge side of the electrostatic cleaner for withdrawing flue gases from the combustion chamber through the high pressure boiler and gas cleaner and discharging them into the stack. There is another blower for forcing air into the combustion chamber.

All three blowers are driven by steam turbines connected across a high pressure steam line from the boiler and a low pressure steam line leading to an air-cooled condenser. A fourth turbine-driven blower, with its turbine also connected across the high pressure and low pressure lines, draws ambient air through the condenser and discharges it into the stack. This turbine is throttled to act as a high pressure regulator between the high pressure and low pressure lines, taking more steamwhen the rate of hot gas production is high and its blower forces more air through the condenser as its speed increases, but when the rate of steam generation slows down, indicative of a lower rate of combustion, the fourth blower slows down, and the condenser requires less cooling air. Generally there is a battery of two or more incinerators discharging into a common stack, and in addition to the blowers referred to other accessory equipment may also be turbinedriven in the same system. In any case the air-cooled condenser-blower arrangement is an important element in the system as a pressure regulator since variations in its speed are not critical to the operation of the incinerator itself. The condensate is of course recirculated as feed water to the high pressure boiler.

Further than this, the preferred embodiment of the invention contemplates a special stack construction wherein there are concentric inner and outer fiues with the hot combustion gases being discharged into the inner one, and the ambient air that has been blown through the condenser being discharged into the outer one. The effect of this is to carry the incinerator gases much higher into the atmosphere than would otherwise be the case, so that they are diffused into the upper air and give less cause for concern to the surrounding residents. In fact, under stagnant atmospheric conditions giving rise to a so-called temperature inversion, this arrangement may be most beneficial, as hereinafter more fully explained.

The present invention has for its principal objects to:

(1) Cool the effluent combustion gases from an incineratorto a temperature compatible with the dust collector and other equipment through which the gases pass to the stack without the usual high consumpion of water or its resulting pollution.

(2) Provide for converting the thermal energy of the combustion gases by generating high pressure steam and utilization of the steam capacity in the operation of the plant independently of any secondary steam load requirement, so that the fuel input to the plant in the form of refuse is not limited by such secondary requirements, or lack thereof. To explain further, if the steam were used to drive a generator, the fuel consumption would be adjusted to the capacity of the generator, whereas by using high pressure steam in turbines to operate the blowers, the steam is converted from high pressure to low pressure, and as above explained, the turbine which cools the condenser is adjusted to regulate the high pressure steam and increase the condensing rate as the volume of steam increases.

(3) The use of excess thermal energy in the stack to carry the combustion products higher into the air, especially when there is a smog causing temperature inversion with the accompanying absence of wind or air currents.

DESCRIPTION OF THE DRAWINGS FIG. 1 of the drawing shows schematically a vertical longitudinal section through a refuse incinerator embodying one form of the invention; and

FIG. 2 is a schematic drawing of the stack for the incinerator illustrating discharge of a double stream of gases from the stack of the incinerator and penetration of an atmospheric inversion layer.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to FIG. 1 of the drawing, there is disclosed a schematic arrangement of the incinerator plant of the invention, wherein the various elements which are of known construction are only diagrammatically shown.

As shown at the left-hand side of FIG. 1, a pusher mechanism 1 feeds miscellaneous municipal refuse through a door 2 into combustion chamber 3 onto a grate structure 4 for combustion of the refuse. Primary and secondary combustion air is supplied from blower 5 through ducts 5x and 5y. Blower 5 is driven by steam turbine 5a. The ash and nonburnable refuse from such combustion is discharged from the grates 4 into a quench tank 6, from which tank 6 the ash is moved by means (not shown) over an inclined surface onto a residue conveyor 7 for disposition. An incinerator of this general construction is show in my patent 2,983,234. There is a baffle structure 6a extending transversely across the quench tank just beyond the combustion chamber on which is supported a high pressure steam boiler 8. The top wall 3a of combustion chamber 3 overlies the waste heat boiler 8 and combines with the combustion chamber and wall 3b in spaced relation thereto to provide a passageway 12 for discharge of products of combustion from the combustion chamber 3 so that the flames and hot combustion gases must flow through the boiler 8 to the passage 12. Between the upper end of passageway 12 and an electrostatic dust precipitator 13, may be mounted a means such as 11 for diffusing ambient air into the still hot gases after they have been initially cooled to some extent by passing through the boiler 8. Such air may be provided by fan 9 through outlet 10. This fan 9 is driven by a steam turbine 5b.

Passageway 12 leads to the inlet end of the electrostatic precipitator 13 or other dry means for removing dust particles from combustion gases passing therethrough and the outlet from the precipitator is connected by conduit 15 to the inlet of an induced draft fan 16. This fan in turn discharges into a conduit 17 leading into the central shaft or flue 18 of a composite stack S. The fan 16 is of a size such as to draw combustion gases from combustion chamber 3 through waste heat boiler 8, precipitator 13 and conduit 15 and to discharge same in conjunction with the natural stack effect from the top of the stack or flue 18 to the atmosphere at a relatively high velocity, for a purpose hereinafter discussed.

In addition to the three fans 5, 9 and 16, there is a fourth fan 30 that draws ambient air through an aircooled condenser 24 and discharges the resulting heated air through duct 22 into the outer flue 23 of the composite stack S, which, as indicated, has concentric inner and outer flues. Fan 30 is driven by steam turbine 5d.

The turbines for the several fans hereinbefore discussed are driven by high pressure steam, generally in excess of 100 p.s.i., from the waste heat boiler 8. Steam line 19 leads from waste heat boiler 8 to a high pressure steam line 20 extending longitudinally above the incinerator. Reading from left to right of FIG. 1, a branch line 2001 delivers high pressure steam from line 20' to steam turbine 5a which is connected with and drives forced draft fan 5. Steam turbine 5b is driven by steam from high pressure branch line 20b for driving fan 9 providing diluent cooling air to the hot gases in advance of precipitator 13 through conduit 10. Steam turbine 50 is driven by steam from branch line 20c to drive high speed fan 16 which draws the cooling air and hot combustion gases from the precipitator through conduit.15 and discharges same through conduit 17 into the central shaft 18 of stack S for discharge to the atmosphere. Steam turbine Ed is driven by steam from high pressure branch line 20d for drawing cooling air through condenser 24 for condensing steam passing therethrough.

Exhaust steam from each of the steam turbines 5a, 5b, 5c and 5d is returned through lines 21a, 21b, 21c, and 21d respectively to a low pressure steam line 21 which in turn discharges into the air-cooled condenser 24, the heated air from which is forced by fan 30 into stack portion 23.

Water in each of the several tubes of the condenser 24 is discharged therefrom through line 25 to a suitable condensate tank 26 from which it is moved by pump 27 to a feed water heater 28 from which it may be returned to waste heat boiler 8 through boiler feed pump 29 and line 31. An auxiliary water-cooled condenser 24a may be provided as indicated, where needed.

A stand-by boiler 32, fired with conventional oil or gas fuel is indicated to the right of FIG. 1 in parallel steam flow with the waste heat boiler 8 for the purpose of plant start-up and to provide supplementary steam generating capacity during periods of combustion of excessively moist, low heat value refuse.

For purposes of simplification, FIG. 1 shows only one furnace unit and associated equipment therefor. Normally several such furnace units would comprise a single plant and the high pressure steam mains, low pressure steam mains and condensate mains for the several units would be interconnected.

Operating balance of the plant is accomplished by means of controlling or resetting the speed governors on the various steam turbines. For simplification the speed regulators are simply indicated in the drawing as valves. The governor 5a of the turbine 5a driving the forced draft fan 5 is manually reset by the plant operator tosuit furnace combustion needs. The governor 5b of the turbine 5b driving dilution air fan 9 is thermostatically regulated to maintain a pre-set temperature level of gases entering the precipitator 13. The governor 5c of the turbine 50 driving induced draft fan 16 may be automatically reset to maintain a present draft or vacuum condition in furnace or furnaces 3. The governor of the turbine 5d driving the condenser fan 30 is automatically reset to maintain the high pressure steam within preset limits. This is indicated by pressure-responsive element 20 that controls air flow to control unit 20d Since the three blowers 5, 9 and 16 are important to the proper functioning of the incinerator, their respective turbines must operate to maintain optimum combustion conditions. The blower 30, which does not directly affect combustion conditions, may operate at variable speeds according to a rise or fall in steam pressure, and therefore function as a pressure regulator for the high pressure steam side of the system. Automatic means, as indicated, responsive to pressure in the high pressure line, may control the throttle for turbine 5d to increasespeed as the rate of steam generation rises and decrease as the rate drops and also compensate for variations in the demands of the other turbines in the system. The increase in speed of blower 30 increases the condensing capacity of condenser 24, so that as the rate of steam production increases and there is an increase in the steam used by turbine 5d, there is an increase in effective condenser capacity.

As previously described, the heated gaseous products from combustion of refuse in combustion chamber 3 are discharged from fan 16 through conduit 17 into the central flue 18 of the stack and the heated air from air-cooled condenser 24 is discharged from fan 30 through conduit 22 into the outer concentric stack flue 23. The large curtain of heated air from stack portion or flue 23 surrounds the hot combustion gases being discharged from flue 18. Since the combustion gases being discharged from the central flue 18 and the warmed air from the flue 23 are both moving upwardly, there is relatively little mixing of the two streams, as compared with the high rate of mixing which would occur between the periphery of a heated jet of gases and a relatively stationary ambient atmosphere, and this is especially so when the velocities of the combustion gas and heated air are comparable. Thus the flue gas discharging from the inner stack or flue 18 at the center of the stream issuing from the stack maintains its high temperature and integrity for a greater vertical distance from the top of stack S than it would if the enveloping warm air curtain from concentric stack portion 23 were not provided, or if the two streams mixed in a single flue. This has the effect, particularly when wind velocity is low, that would be achieved by a much higher stack in carrying the combustion products hgher into the atmosphere'.

In conditions when there is a so-called temperature inversion during which atmospheric pollution along with smog increases rapidly, with a cloud layer at a level of around 1000 to 1200 feet above the ground, it has been observed and photographed that the cloud layer above the smoke stack of a power station may have a cumuluslike appearance indicative of an attempt by the rising warm air from the stack to break through the inversion layer. It is believed that the present invention will result not only in the combustion gases being carried to a higher level before they disperse into the atmosphere, but that during such periods of inversion they may have sufiicient velocity and heat energy to break through the inversion level so as to avoid adding any pollution to the surface atmosphere, and possibly aid in inducing a flow of surrounding air above this layer and contribute by such disturbance to relief from smog-producing conditions.

As is well known, such conditions arise over an area when there is a high pressure mass over it accompanied by a very low wind velocity or calm, and the overlying air mass is warmer than the air beneath so that instead of air being warmed by contact with the ground and rising to the cooler air above in the normal manner, the earth layer is not warmed sufiiciently to penetrate the overlying warm air mass and the air stagnates, and accumulates the pollution generated at or near the surface. As indicated above, it is contemplated that with a stack of the order of 100 feet or so the inner core of relatively high velocity hot gases, .protected by the surrounding air which has been warmed by transfer of heat from the very hot furnace gases to the boiler to generate steam and the heat then recovered for use in the stack by heating ambient air by condensing the steam will be especially helpful in pene trating the inversion layer so that the combustion gases will not pollute the air below the inversion layer and the continued penetration of the inversion layer by the hot gases may even induce the upflow of the surrounding air and accelerate the dispersion of the atmospheric inversion.

This is illustrated in FIG. 2 wherein the almost columnar flow of the hot inner core of combustion gases travels upwardly within a surrounding envelope of upwardly-moving warm air and the turbulence between the moving and stationary air tending to otherwise cause immediate mixing of the stack gases and the ambient air is largely confined, at least for the first substantial portion of the upward travel, to the warm air envelope, and the more nearly the velocity of the outer envelope approaches the velocity of the inner column, the higher this effect will continue. The condition is generally comparable to the observed laminar flow of fluids in a conduit, or in a river where the mid-stream flows faster than the water along the banks due to the drag which the shore exerts on the moving stream.

In FIG. 1 of the drawings, the incinerator exterior walls are merely indicated by line drawings, but it is to be understood that they are of the usual refractory construction commonly employed in the art.

It will be seen, therefore, that the gases are cooled and cleaned without the use of water in the usual way, and that a substantial amount of the heat so removed, after providing power to operate various elements of the incinerator plant, is returned to the stack for adding to the stack draft. The steam turbine system as described makes the plant relatively independent of any secondary power sources, and the high pressure steam system is self-regulating. Moreover the composite stack in conjunction with the provision of means for recuperating some of the combustion gas heat and returning it to the stack as heated air and recuperating some of it as mechanical energy to move this air has the beneficial effect of carrying the combustion gases higher into the atmosphere before they difluse into the atmosphere, giving the benefit in this respect of a much higher stack, especially when the air is relatively calm and the gases otherwise would be most objectionable. Especially is this stack arrangement and heat recuperating system believed tobe of advantage where there is a temperature inversion over the area.

I claim:

'1. In an incinerator plant having an incinerator with a combustion chamber, a combustion gas discharge duct through which combustion products are conducted from the combustion chamber and a stack, the invention comprising:

(a) a waste heat boiler for removing heat from the combustion gases arranged so that combustion gases pass therethrough in flowing from the combustion chamber tosaid duct,

(b) a dry dust precipitator in said duct between the boiler and the stack,

(c) a draft-inducing fan in said duct between the boiler and the stack, the precipitator and fan being so arranged that partially cooled gases after passing through the boiler pass in succession through one and then the other,

((1) a turbine for driving said fan,

(e) a blower for supplying combustion air to the incinerator,

(f) a turbine for driving said blower,

(g) a steam condenser,

(h) a blower and turbine for driving the same for blowing ambient air through said condenser and a duct for conducting air that has been moved by said blower through the condenser into the stack,

(i) means for conducting high pressure steam from the boiler to each of said turbines to drive the same,

(j) means for conducting low pressure steam discharged by the several turbines to the condenser whereby some heat removed from the combustion gases is returned as heated air to the stack, and

(it) means for returning condensate from the condenser as feed Water to the boiler.

2. The invention defined in claim 1 in which the turbine for moving air through the condenser is arranged to operate as a pressure regulator to vary the speed of the blower directly as the steam generated in the boiler increases or decreases.

3. The invention defined in claim 1 wherein there is also blower means in said duct between the boiler and the precipitator and fan for introducing cooling air into said duct, with a turbine for driving said last-named blower means operatively connected across the said high pressure steam-conducting means and said low pressure steam-conducting means.

4. The invention defined in claim 3 in which each turbine has valve means for independently controlling its speed.

5-. The invention defined in claim 1 in which the stack has concentric inner and outer fines and the duct from the combustion chamber discharges into the inner flue and the duct from the blower which moves air through the condenser discharges into said outer fine 6. An incinerator plant comprising an incinerator, a stack having inner and outer concentric flues, a duct arranged to conduct hot gases of combustion from the incinerator and discharge them into the inner fine, a high pressure boiler so located that combustion gases from the incinerator flow through said boiler to partially cool the gases and generate steam, and means arranged to heat air with at least some of the steam and discharge the heated air into the outer flue of said stack whereby the combustion gases leave said stack as a columnar flow surrounded by a rising zone of heated air.

-'7. The method of discharging hot combustion gases into the atmosphere which comprises conducting hot combustion gases into the central core region of a stack; heating clean air; discharging the heated clean air into an outer zone of such stack whereby the air and gases leave the stack as a columnar flow with the gases surrounded by a rising envelope of heated air and the combustion gases are carried into the atmosphere higher above the stack during periods of calm before diffusing into the air than if said columnar flow were not provided.

8. The method defined in claim 7' including the steps of extracting heat from combustion gases in a steam boiler prior to said conducting step; and directing the steam generated during said extracting step to heat the air during said heating.

References Cited KENNETH W. SPRAGUE, Primary Examiner US. Cl. X.R. 

